The realization of greater capacity in today's wireless communications environments may require the achievement of a consistently higher signal to interference-plus-noise ratio (SINR) over a significant percentage of a cell's coverage area. Yet achievement of such a goal will require, in general, smaller cells or alternatively, operation in a smaller region of a cell when operating at a given transmit power level. Hence, the current network model of higher-power outdoor macro cells will need to be augmented by lower-power indoor and outdoor micro- and pico-cells. While such a move towards smaller cells will significantly increase the number of access points within a cellular system, it will also lead to significant coverage overlap, both planned and unplanned, between cells.
Co-ordination of transmission and reception in today's cellular systems has been designed with the philosophy of “smart network, dumb user equipment,” reflecting the telephone-centric mindset of a previous era. The “smart” network model is based on the premise that the network has a global view, and overall control, of everything that is occurring within the network. However, this assumption breaks down in a heterogeneous coverage environment as it is likely that no single, centralized network entity will have a global view and overall control. As an example, transmission and reception within a given cell is coordinated by the Access Point (AP) responsible for that cell. However, operation across cell boundaries may be un-coordinated due to different administrative domains or to difficulties encountered when communicating between APs. As a consequence, completely un-coordinated operation may ultimately result in unacceptable levels of interference that could negate the benefits of improved signal levels garnered through the use of smaller cells.